It's not possible to be conclusive from the trailer - Donna may be speaking metaphorically about the "right man" - but sadly it does appear that she's going to be besotted with the Doctor. I honestly can't imagine him reciprocating - more like charging full pelt in the opposite direction. But maybe I'm projecting.

Certainly in the old Who there were many companions without a trace of romance, but in the new 'sexier' Who it seems to be designed-in. It's as if it worked once with Rose and now they daren't get rid of it in case the audience rebels.